DESCRIPTION: Past studies have demonstrated the 5HT modulates different ion currents in the DRG cell bodies of sensory neurons which likely transmit different kinds of sensory information. Thus, it appears possible that 5HT modulates different types of sensory information in different ways. This study will expand on previous work by subdividing DRG cell bodies into groups based on functionally relevant criteria and examining the serotonergic modulation of ion currents in the different groups. DRG cells with sensory receptors in skin, skeletal muscle or viscera will be detected by labeling nerves serving these different tissues with fluorescent neuronal tracer. DRG cells will also be subdivided based on the expression of various carbohydrate surface antigens, which are expressed by different populations of sensory neuron that terminate in different laminae of the spinal cord and thus likely transmit different types of sensory information. In addition, conduction velocity of attached axons will be used to subdivide DRG cells into C, Adelta and Aalphabeta groups which encompass different subpopulations of identified sensory afferents. DRG cells categorized using the above criteria will be further characterized regarding sensitivity to capsaicin, which targets mainly nociceptors. The distribution of ion currents and their modulation by 5HT will be studied in groups delineated by functional criteria, in order to better understand how 5HT might affect different types of sensory information. It will frequently be possible to record all of the mentioned ion currents in individual DRG cells. This will aid in the identification of ion channels whose expression has a predictive value regarding modulator effects of 5HT. Also, reoccurring unique patterns of ion channel expression may be observed which could possibly be attributed to groups of highly related sensory neurons or specific individual types of sensory neurons. It is possible that there is a unique DRG cell body type corresponding to each type of peripheral sensory receptor. A better understanding of the serotonergic modulation of ion channels in sensory neurons which transmit different types of information will aid in the development of new pharmacological agents for the control of pain.